1. Field of the Invention
The present invention relates to a hard disk drive, and in particular, to a circuit for protecting circuit parts from overvoltage and surge voltage in a hard disk drive.
2. Description of the Related Art
Recently, a data storing and reading device has rapidly been developed toward large capacity and high-speed data access to satisfy demands for a multimedia system. One of such data storing and reading devices is a hard disk drive, which is widely used as an auxiliary memory device for a computer system due to its advantages of high-speed data access and large capacity. This hard disk drive generally uses two power supplies, for example, +5 V and +12 V. That is, the hard disk drive includes a +5 V power supply input terminal for receiving +5 V as an operational power supply voltage of interior circuit devices, and a +12 V power supply input terminal for receiving +12 V as a device driving power supply voltage. A protection circuit may intervene between the +5 V power supply input terminal for receiving +5 V and circuit parts operated at +5 V in the hard disk drive, to prevent damage to the circuit parts. Such protection circuits include a fuse for sensing and blocking an overvoltage, a ferrite bead for replacing the fuse or filtering a power supply, and a noise filter having a resistor and a capacitor, for removing noise from a power supply.
Such protection circuits are not effective in protecting interior circuit parts in a hard disk drive against a surge voltage applied in several tens of milliseconds, since, for example, a fuse is shorted in several seconds regardless of the current sensing capability of the fuse. That is, with a surge voltage applied, the fuse is shorted after the circuit parts are damaged. Such problem arises from designing the protection circuits for a stable power supply environment, not compatible with an unstable power supply varying environment.
Protection circuits for protecting against overvoltages are known. One such protection circuit is described by Pierre Rault in U.S. Pat. No. 5,751,531 entitled Protection Circuit Against High Energy Overvoltages, Having A Controlled Clipping Voltage.